backport_pr: get Head object from `new_branch` name after creation
backport_pr: get Head object from `new_branch` name after creation

mfrey/RIOT,miri64/RIOT,rfuentess/RIOT,authmillenon/RIOT,rfuentess/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,smlng/RIOT,cladmi/RIOT,ant9000/RIOT,authmillenon/RIOT,jasonatran/RIOT,mfrey/RIOT,x3ro/RIOT,ant9000/RIOT,yogo1212/RIOT,mtausig/RIOT,smlng/RIOT,kaspar030/RIOT,miri64/RIOT,authmillenon/RIOT,yogo1212/RIOT,OTAkeys/RIOT,kYc0o/RIOT,ant9000/RIOT,mtausig/RIOT,cladmi/RIOT,kYc0o/RIOT,miri64/RIOT,RIOT-OS/RIOT,mfrey/RIOT,toonst/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,josephnoir/RIOT,OlegHahm/RIOT,toonst/RIOT,yogo1212/RIOT,josephnoir/RIOT,kYc0o/RIOT,smlng/RIOT,aeneby/RIOT,toonst/RIOT,cladmi/RIOT,OTAkeys/RIOT,yogo1212/RIOT,ant9000/RIOT,OlegHahm/RIOT,authmillenon/RIOT,OlegHahm/RIOT,x3ro/RIOT,RIOT-OS/RIOT,basilfx/RIOT,mfrey/RIOT,miri64/RIOT,mtausig/RIOT,aeneby/RIOT,josephnoir/RIOT,kYc0o/RIOT,rfuentess/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,basilfx/RIOT,yogo1212/RIOT,basilfx/RIOT,kYc0o/RIOT,x3ro/RIOT,kaspar030/RIOT,OTAkeys/RIOT,cladmi/RIOT,aeneby/RIOT,josephnoir/RIOT,x3ro/RIOT,smlng/RIOT,jasonatran/RIOT,rfuentess/RIOT,jasonatran/RIOT,miri64/RIOT,authmillenon/RIOT,aeneby/RIOT,ant9000/RIOT,smlng/RIOT,cladmi/RIOT,yogo1212/RIOT,josephnoir/RIOT,basilfx/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,mfrey/RIOT,OTAkeys/RIOT,mtausig/RIOT,OlegHahm/RIOT,x3ro/RIOT,toonst/RIOT,basilfx/RIOT,rfuentess/RIOT,jasonatran/RIOT,jasonatran/RIOT,mtausig/RIOT,toonst/RIOT,aeneby/RIOT